The subject of the present invention is a calibration method in a machine for processing plate elements, and a machine for processing plate elements using said method.
Such machines are used in particular in the printing and packaging industry, for example for the manufacture of cardboard boxes from plate elements such as sheets of preprinted cardboard. In an introduction station, these sheets are taken from a stack situated upstream of the machine, and are then positioned by an introducer in gripper bars mounted at regular intervals on a subsequent line of endless chains. The latter makes it possible to convey the sheets into the various later processing stations of the machine. Typically, such stations are devoted to cutting the sheets, ejecting the cutting waste and receiving these sheets in a stack.
In a rhythmical motion, the line of chains moves and stops periodically so that, during each movement, all the gripper bars engaged with a sheet are passed from one station to the adjacent station downstream. If it is desired to obtain a print or a quality conversion, the positioning of the sheets within the various successive stations is a fundamental operation. For the cutting of a printed sheet, it will be understood that the positioning of the sheet in the cutting station must be precise. Specifically, it is appropriate to ensure that the tools used for cutting, for example the form to be cut of a platen press, are in perfect register with the print that has previously been made on the sheet.
Patent CH 690,470 describes a device for ensuring the quality of production of a press for making packages. To do this, this device comprises a camera designed to read on the one hand location marks associated with the printing, and on the other hand a mark intended for locating the cutting position. These location marks are placed on the front spoil of the sheet held by the gripper bar. The cutting mark is made by means of a perforator secured to the cutting tools. This perforator arranges a hole in the front spoil of the sheet at the same time as the latter is cut. Further downstream, another device makes it possible to mark the sheets identified as being faulty by the camera, namely those which have an out-of-tolerance offset between the printing and the cutting.
Patent EP 1,044,908 relates to a device and a method for positioning plate elements in an introduction station. From a bed situated in a rear starting position, this method consists in engaging means for fastening a plate element to the bed, then in commanding actuators to allow its movement forward depending on the position of the plate element on the bed. Accordingly, the front edge of the plate element is brought forward, stopped and then released in a predetermined position in the grippers of the gripper bar of the conveyor device before the bed has been finally returned to the start position. In order to be able to move the bed forward, if necessary sideways or obliquely, by an adequate amount, optoelectronic means read the coordinates of the position of the plate element and calculate the movement necessary to be able to position it as correctly as possible in the gripper bar.
The processing of a batch of identical plate elements, that is to say of the same dimensions, consisting of the same material and bearing the same prints is called a job. When the operator carries out a new job on the machine, he begins by calibrating the sensors which are used to detect the various location marks printed on the plate elements. This operation requires operator expertise, takes time and consumes plate elements in order to carry out the various tests until an acceptable result is obtained.